IN VIVO MODULATION OF POLO-LIKE KINASES SUPPORTS A KEY ROLE FOR PLK2 IN SER129 α-SYNUCLEIN PHOSPHORYLATION IN MOUSE BRAIN

alpha-Synuclein is the major component of Lewy bodies. alpha-Synuclein phosphorylated at Ser 129 (Phospho-alpha-Syn) is the most common synuclein modification observed in Parkinson's disease pathology and transgenic animal models. Polo-like kinase 2 (PLK2) was previously proposed as an important kinase in alpha-synuclein phosphorylation at Ser129. To better understand the role of PLK2 in alpha-synuclein phosphorylation in vivo, we further evaluated the effect of PLK2 genetic knockdown and pharmacological inhibition on Phospho-alpha-Syn levels in different brain regions of PLK2 knockout (KO), heterozygous (Het) and wild-type (WT) mice. Whereas PLK2 knockdown had no effect on Total-alpha-synuclein brain levels, it resulted in a gene-dosage dependent, albeit incomplete, reduction of endogenous Phospho-alpha-Syn levels in all brain regions investigated. No compensatory induction of other alpha-synuclein kinases (PLK3, casein kinase-2, G-protein-coupled receptor kinase 5 (GRK5) and GRK6) was observed at the mRNA level in the PLK2 KO mouse brain. To determine whether increased activity of another PLK family member is responsible for the residual Phospho-alpha-Syn levels in the PLK2 KO mouse brain, the pan-PLK inhibitor BI 2536 was tested in PLK2 KO mice. Whereas BI 2536 reduced Phospho-alpha-Syn levels in WT mice, it did not further reduce the residual endogenous Phospho-alpha-Syn levels in PLK2 KO and Het mice, suggesting that a kinase other than PLK1-3 accounts for the remaining PLK inhibitor-resistant pool in the mouse brain. Moreover, PLK3 KO in mice had no effect on both Total- and Phospho-alpha-Syn brain levels. These results support a significant role for a PLK kinase in phosphorylating alpha-synuclein at Ser129 in the brain, and suggest that PLK2 is responsible for this activity under physiological conditions. (C) 2013 IBRO. Published by Elsevier Ltd. All rights reserved.